1. Field of the Invention
The present invention relates generally to injection molding and, more particularly, to a mold assembly for use in an injection molding machine, wherein the mold assembly incorporates one or more valve gates having replaceable, drop-in actuators.
2. Discussion of the Prior Art
Injection molding machines are known which include a base on which a pair of relatively movable platens are supported. Typically, one of the platens is fixed on the base while the other is movable back and forth relative to the fixed platen. An example of an injection molding machine of this general type is marketed under the trademark TM-300G.TM. by Toyo Machinery & Metal Co., Ltd., and includes an extruder positioned in line with the fixed platen for supplying moldable material to a mold assembly positioned between the platens. The extruder includes an outlet nozzle extending through the fixed platen so that material supplied by the extruder can be directed into the mold assembly.
Conventionally, a mold assembly adapted for use in this known type of molding machine includes a cavity plate presenting several mold cavities, and a core plate presenting a similar number of cores aligned with the cavities. The cavity plate is typically secured to the fixed platen of the machine along with a manifold housing that includes a manifold for directing the moldable material from the extruder into each of the cavities of the cavity plate. The core plate is secured to the movable platen so that it can be pulled away from the cavity plate upon completion of molding to remove the molded parts from the cavities, and a knockout means is provided for then releasing the molded parts from the cores. In addition, separable thread splits can be provided that are also carried along with the core plate and cooperate with one another and the cavities to define the outer shape of the part to be molded.
In order to control the flow of moldable material into the cavities of the mold assembly, it is known to provide a nozzle at the inlet to each cavity in the cavity plate, and a valve gate at each nozzle for controlling the flow of moldable material from the nozzle. Each valve gate includes an elongated stem extending into the mouth of one of the nozzles and being movable between flow-blocking and flow-permitting positions. An actuator is also provided in association with each valve gate for moving the valve gate between these positions, and typically includes a fluid actuated actuator or the like.
An example of a known valve gate mechanism includes a fluid motor comprised of a cylinder that is removably seated in a bore of a clamp plate that is spaced from the mold manifold. A piston is mounted in the cylinder and includes a stepped bore in which the valve gate stem is retained. The piston also includes a guide portion that extends from the bore toward the manifold through a guide member that is sandwiched within the bore between the cylinder and the clamp plate. The clamp plate is formed with a pair of passageways that are adapted to align with ports formed in the cylinder on either side of the piston so that fluid can be supplied to the cylinder in order to reciprocate the piston back and forth, actuating the valve gate. One of the passageways communicates with the cylinder through a hole in the cylinder wall while the other passageway connects with a hole in the guide member. Annular seals extend around the cylinder above and below the hole in the cylinder wall for sealing the space between the cylinder and the clamp plate, and an additional seal is provided between the guide member and the clamp plate for sealing the space therebetween.
Numerous problems arise in the use of mold assemblies incorporating conventional valve gate actuator constructions. For example, known actuators are formed of several parts that must be assembled on the clamp plate within each bore, and it is not possible to test the actuators for a good seal until all of them have been assembled and actuated at the operating temperature of the mold assembly. Thus, in a 32-cavity mold assembly, it is necessary to assemble all 32 actuators before any one of them can be tested to determine the operability thereof. This represents a significant investment of both time and effort during assembly of the mold and fails to provide immediate confirmation to the operator that each actuator has been properly assembled.
If during the life of the mold assembly a seal goes bad or it is necessary to replace any other component of an actuator, it is necessary in the conventional construction to disassemble the bad actuators from the clamp plate, repair or replace the bad components, and then reassemble the actuator in the clamp plate. During this process, the entire mold assembly remains out of service, representing potentially expensive down time for the machine. Further, it is not possible to test the repaired or replaced components of the actuator until the components are reassembled in the clamp plate and tested at molding temperature. Thus, if one or more of actuators are not properly sealed, it is necessary to repeat the mentioned process until proper operation is achieved.